Hydration Processes Of Barium Chloride: Size-Selected Anion Photoelectron Spectroscopy And Theoretical Calculations Of Bacl2-Water Clusters

In order to understand the hydration processes of BaCl2, we investigated BaCl2(H2O)(n)(-) (n = 0-5) clusters using size-selected anion photoelectron spectroscopy and theoretical calculations. The structures of neutral BaCl2(H2O)(n) clusters up to n = 8 were also investigated by theoretical calculations. It is found that in BaCl2(H2O)(n)(-/0), the Ba-Cl distances increase very slowly with the cluster size. The hydration process is not able to induce the breaking of a Ba-Cl bond in the cluster size range (n = 0-8) studied in this work. In small BaCl2(H2O)(n) clusters with n <= 5, the Ba atom has a coordination number of n + 2; however, in BaCl2(H2O)(6-8) clusters, the Ba atom coordinates with two Cl atoms and (n - 1) water molecules, and it has a coordination number of n + 1. Unlike the previously studied MgCl2(H2O)(n)(-) and CaCl2(H2O)(n)(-), negative charge-transfer-to-solvent behavior has not been observed for BaCl2(H2O)(n)(-), and the excess electron of BaCl2(H2O)(n)(-) is mainly localized on the Ba atom rather on the water molecules. No observation of Ba2+-Cl- separation in current work is consistent with the lower solubility of BaCl2 compared to MgCl2 and CaCl2. Considering the BaCl2/H2O mole ratio in the saturated solution, one would expect that about 20-30 H2O molecules are needed to break the first Ba-Cl bond in BaCl2.